Meat Casseroles These thickeners should be added to room temperature liquids, stirred, and then incorporated to avoid lumps. All purpose flour Cornstarch Cheesy Casseroles A great option for thickening cream and dairy-based casseroles. Cornstarch Vegan, Non-dairy Casseroles These are great options for lighter casseroles--and they’re all gluten free! Potato starch Chickpea flour Arrowroot powder Agar Ground flaxseeds Kosher Casseroles Great for Passover casseroles and sauces. Note: Do not add to liquids before boiling as it will lose its thickening power. Potato starch